Self-processing photographic film units are now available which are completely self-contained and are adapted to be employed in a camera in which the film unit is exposed and then processed by moving it between a pair of pressure-applying members. The components of the film unit are assembled to form an integral structure and the integrity of this structure is maintained during exposure, processing and viewing, thereby making it unnecessary to store, handle and/or move separately, individual elements of the film unit, and minimizing the complexity of the structure required to contain and manipulate the film unit to effect exposure and processing thereof. Such a film unit structure is attractive, includes a minimum of simple and easily assembled components, is of a minimum size in relation to image size and generally includes substantially no excess materials. The film unit includes a container of the processing fluid and means for promoting and facilitating spreading of the fluid in a layer of predetermined depth and extent.
Such film units generally comprise two separate, flexible sheetlike elements including a first or image-recording sheet including a layer containing a photosensitive image-recording material and a second sheet for aiding in the distribution of a viscous liquid processing agent as a layer in contact with an exposed area of the photosensitive material. The supports of the sheets are both transparent to provide for exposure of the photosensitive material through the second sheet support while the sheets are in superposition, and to provide for viewing the image formed through the first sheet support. The two sheets are secured to one another at their lateral margins to form an integral unit, the integrity of which is established prior to loading into a camera, is maintained throughout exposure and processing and can be maintained subsequent to processing.
The film unit further includes a rupturable container filled with a fluent processing composition, the container being conveniently formed from a rectangular blank of a multilayer, fluid impermeable sheet material folded medially upon itself to form two walls sealed to one another along three sides to form an elongated cavity, or a plurality of cavities, filled with the fluent processing composition or liquid. The container usually includes elongated transverse marginal sections and end marginal sections, the seal between the transverse marginal sections being weaker than the seal between the end marginal sections so as to become unsealed and form one or more fluid discharge passages in response to pressure generated within the fluid contents of the container as a result of the application of compressive pressure to the walls of the container. The fluid-filled cavity is formed by medial sections of the container walls that are bellied outwardly so that when the container is flattened by progressively applying compressive pressure its fluid contents are ejected. As the viscous fluent processing composition is discharged from the container, it is spread from the leading end of the film unit between the sheets toward the trailing end thereof to form a substantially uniform layer between the sheets. Excess processing fluid is then trapped and retained within the film unit at the trailing end thereof. The processing fluid includes, in addition to the reagents required to produce a diffusion transfer image, a thickening or film-forming agent provided to aid in the formation of a layer or film of the fluid between sheets, and an opacifying agent.
In prior art film units of the general type described above, various means have been provided for holding the two sheets together. Such joining means generally comprise an element which couples the sheets of the film units together. Examples of such coupling elements are illustrated in U.S. Pat. Nos. 3,748,139, 3,764,332, 3,775,127 and 2,500,422. The joining means disclosed in the first two references included a masking element which is coupled to the inner surface of the periphery of the two superposed sheets by layers of adhesive. This masking element has a substantially uniform thickness which necessitates the use of recessed or stepped pressure members to achieve the desired processing fluid thickness. Moreover, to avoid undesirable effects along the periphery of the image area it is necessary to regulate the thickness of the processing fluid at the periphery of the image area within very close tolerances. One method of preventing such edge defects from detracting from the photographic image is disclosed in U.S. Pat. No. 3,775,127, wherein a very thin mask coating is applied to one of the sheets to form the periphery of the visible image with the lateral edges of the sheets being adhesively coupled substantially directly together by narrower strips of adhesive along the outer lateral edges. This construction also required the use of recessed or stepped pressure members or rollers.
Other prior art constructions have utilized a thin mask in conjunction with separately applied spacer members along the lateral edges of the film unit to hold the sheets together. Such constructions have overcome the problem of edge defects appearing around the visible image since the processing fluid extends behind the mask to the thicker spacer members, but have been generally more difficult to assemble in view of the close tolerances necessary in applying the spacer members accurately in registration with the mask. Moreover, it is difficult to automatically and mechanically handle such small thin, separate spacer members.
Another approach to joining the two sheets is illustrated in U.S. Pat. No. 2,500,422, wherein an external binder element is employed which is wrapped around all four edges of the two sheets and is secured to the outer surfaces of the sheets to maintain them in registration. Such a construction solves some of the problems of edge defects since it is possible for the processing fluid to spread behind the inner periphery of the binder element so that any edge defects occur between the wrapped-around portions of the binder element. However, such a construction has the disadvantage that the choice of the material and the color of the binder element is limited to that which is acceptable at the viewing face of the picture unit since a portion of the binder element frames the viewing surface of the picture. Also, the use of such a binding element provides a viewing surface which is not planar and which has a portion that can become frayed and unsightly with handling. Moreover, the use of such external binding elements can, in some instances, necessitate the embossing of one or both of the sheets to provide satisfactory spreading of the processing fluid. More significantly, the use of such external binders complicates the assembly of such film units in that it is not possible to assemble the film units by joining substantially continuous webs of the two sheet materials to the binder element and subsequently chopping individual film units from the composite web. While it is relatively simple to provide a binder which is wrapped around the portion of the picture units which form the edges of the continuous composite webs, it is not possible to provide a binder which is wrapped around the edges of adjacent film units which are formed as they are chopped from a continuous web, i.e., the edges which are transverse of the web. It is necessary to space on the binder web the sheets forming one film unit from the sheets forming the next adjacent film unit to provide the necessary length of binder therebetween which can be cut and then wrapped around the adjacent edges of each of the finished film units after the continuous web has been chopped into individual film units. Accordingly, it is necessary to utilize a less efficient method of assembling such film units utilizing a continuous web of the binder element material, and disposing discrete sections of superposed sheets at spaced locations on the web, which superposed sheets must be accurately positioned with regard to the binder web and must be maintained in superposition and alignment with respect to each other while the various assembly operations are performed. This, of course, complicates and increases the cost of such film unit fabrication.